Field of the Invention
The present invention generally relates to a copying apparatus and, more specifically, to a copying apparatus having a function of forming color copies as well as a function of forming outline images. Description of the Prior Art
Recently, devices capable of forming not only black images but color images such as red, blue and so on have been developed in the field of image forming apparatuses such as copying machines employing electrophotography process. More specifically, a plurality of developing devices are arranged around a photoreceptor, and a color developing device containing developer with color toner can be selectively mounted and used by replacing other color developing devices.
In consideration of the recognization that an outline of an image is very important, comprising much information and representing characteristics of the image, the applicants of the present application have proposed a method for forming an outline image, in which a second charging apparatus is provided between an image exposing apparatus and a developing device, and only outlines of a picture are extracted to form outline images, and line images are directly reproduced as the line images by the operation of the second charging apparatus (disclosed in USSN Nos. 16,716 and 16,717).
Let us consider a case in which a function of forming outline images is implemented in a unit (hereinafter referred to as an outline unit) compatible with the developing devices, and the unit is mounted on a copying machine capable of mounting a plurality of developing devices. In that case, the outline unit should be arranged on the upstream side of developing devices in the direction of movement of the photoreceptor. If three or more developing devices are mounted to turn the latent electrostatic images of the outline portions to toner images, the outline unit should be arranged on the upstream side of the developing devices so as to enable selection of developing devices arranged on the downstream side of the outline unit, to prevent the generation of miscopies.
Conventionally, the selection of developing color is carried out by searching all mounted developing devices one by one. Sometimes erroneous selection results from this process.